Mineral Nutrition - Overview 1. Some minerals can be used as is: e.g. K + ions for guard cell regulation 2. Some minerals have to be incorporated into other compounds to be useful: e.g. Fe + in the cytochrome complex of the light reactions 3. Some mineral compounds have to be altered to be useful: NO 3 - must be converted to NH 4 + inside the plant
Chemical composition of plants 1. 80–85 % of an herbaceous plant is water. 2. Water is a nutrient since it supplies most of the hydrogen and some oxygen incorporated into organic compounds by photosynthesis. 3. But > 90% of the water absorbed is lost by transpiration. 4. Water’s primary function is to serve as a solvent. 5. Water also is involved in cell elongation and turgor pressure regulation
1. 95% “organic” – C, H, O from air & water, assimilated by photosynthesis 2. 5% inorganic minerals Chemical composition of plants: dry weight
1. Nutrients that are required for a plant to grow from a seed and complete its life cycle. 2. 2 types: macronutrients & micronutrients Essential Nutrients
1.Elements required by plants in relatively large amounts. Macronutrients CHOPKNS Ca Mg
Macro- nutrient Form available to plants Major functions CarbonCO 2 Organic compounds HydrogenH20H20Organic compounds OxygenCO 2 (air), O 2 (soil) Organic compounds PhosphorusH 2 PO 4 -, HPO 4 2- Nucleic acids, phospholipids, ATP PotassiumK+K+ Water balance (stomata), protein synthesis NitrogenNH 4 +, NO 3 - Proteins, nucleic acids, hormones, chlorophyll SulfurSO 4 2- Proteins CalciumCa 2+ Cell walls & membranes, enzyme activation MagnesiumMg 2+ Chlorophyll, enzyme activation
Micronutrients 1. These elements are required by plants in relatively small amounts (<0.1% dry mass). 2. Major functions: A. cofactors of enzymatic reactions B. Light reactions of photosynthesis C. Optimal concentrations highly species specific Fe, B, Cl, Mo, Cu, Mn, Ni, & Zn
dependent on: 1. the role of the nutrient in the plant 2. its mobility Mineral Deficiencies
Immobile Nutrients 1. Once they have been incorporated into plant tissue, they remain (can’t return to phloem). 2. Boron, calcium, and iron 3. Growth = normal until the mineral is depleted from soil; new growth suffers deficiency and thus youngest tissues show symptoms first.
Mobile Nutrients 1. can be translocated by phloem to younger (actively growing) tissue. 2. Cl, Mg, N, P, K, and S 3. When mineral is depleted, nutrients translocated to younger tissue. 4. Thus older tissues show deficiency & then die What is the adaptive value of nutrient mobility?
Mineral Deficiency 1. Not common in natural populations. Why? A. Plants have adapted to soil components 2. Common in crops & ornamentals. Why? A. Human selection for biggest, fastest plants. Need more nutrients than the soil provides B. Crop growth depletes the soil because no organic matter return 3. Deficiencies of N, P, and K are the most common. 4. Shortages of micronutrients are less common and often soil type specific. 5. Overdoses of some micronutrients can be toxic.
Mineral Deficiency Symptoms 1. Chlorosis – leaves lack chlorophyll: yellow, brittle, papery. Typically lack of N or Fe. 2. Necrosis – the death of patches of tissue 3. Purpling – deficiency of N or P, causes accumulation of purple pigments 4. Stunting – lack of water, N
Soils 1. What do soils give to plants?? A. minerals B. nitrogen–fixing bacteria C. mycorrhizal fungi D. water E. oxygen
Soil properties influence mineral nutrition 1. Chemistry – determines which minerals are present and available, thus affecting plant community composition 2. Physical nature – affects porosity, texture, density of soil, which affects #1 3. Soil organisms – A. decomposition & mineral return B. Interact with roots to make nutrients available C. Nitrogen! The only mineral that the plant can ONLY get from reactions mediated by soil organisms.
Large, spaces for water & air Small, more SA for retaining water & minerals Soil texture & composition 1. Soil is created by weathering of solid rock by: water freeze/thaw, leaching of acids from organic matter, carbonic acid from respiration + water. 2. Topsoil is a mixture of weathered rock particles & humus (decayed organic matter). 3. Texture: sand, silt, clay
More about topsoil….. 1. Bacteria, fungi, insects, protists, nematodes, & Earthworms! Create channels for air& water, secrete mucus that binds soil particles 2. Humus: reservoir of nutrients from decaying plant & animal material 3. Bacterial metabolism recycles nutrients
Availability of soil nutrients 1. Cations in soil water adhere to clay particles (negatively charged surface) 2. Anions do not bind; thus they can leach! (NO 3, HPO 4, SO 4 ) 3. Cations become available for root uptake by cation exchange – H + displaces cations on the soil particle surface 4. H+ from carbonic acid – formed from water + CO 2 released from root respiration 5. Humus – negatively charged & holds water & nutrients. Thus very important in the soil!!!!!
Thus soil pH is important! 1. Low pH = high H + concentration A. More cations released B. Too much acid – cations leach…..mineral deficiency 2. High pH A. Not enough H + for cation release….mineral deficiency
Why nitrogen? 1. Air is 80% Nitrogen, but….. 2. Macronutrient that is most often limiting. Why? Is almost always taken up as anions (NO 3 - ) 3. What’s it used for? Proteins (AAs), nucleic acids, chlorophyll production
The Nitrogen Cycle Organic N NH 4 NO 3 Decomposition N2N2 Ammonification Nitrification Immobilization Uptake Leaching Denitrification N 2 fixation
Nitrogen Metabolism in Plants 1. Steps: A. N fixation – conversion of N 2 to NH 3 B. Ammonification – conversion of NH 3 or organic N into NH 4 + C. Nitrification – conversion of NH 4 + to NO 3 - D. N reduction – conversion of NO 3 - back to NH 4 + within plant. E. N assimilation – incorporation of NH 4 + into AAs, nucleic acids of the plant
But N is also lost…. 1. Leaching – loss of NO 3 - by soil water movement 2. Denitrification – conversion of NO 3 - back to N 2
Fig 37.9 All steps within the soil are mediated by bacteria!!!!
A. Nitrogen Fixation This process is catalyzed by the enzyme nitrogenase, requires energy (ATP), and occurs in three ways: a. Lightening – converts N in air to inorganic N that falls in raindrops b. Non-symbiotic – certain soil bacteria c. Symbiotic
c. Symbiotic Nitrogen Fixation * Legumes: peas, beans, alfalfa *The legume/bacteria interaction results in the formation of nodules on roots *Plant – gets ample inorganic N source *Bacteria – gets ample carbon source
d. Fixation in Nonlegumes * Here in the NW: alder * Azolla (a fern) contains a symbiotic N fixing cyanobacteria useful in rice paddies. * Plants with symbiotic N fixers tend to be first colonizers. Why?
a. Unfortunately NH 4 + is a highly desirable resource for free–living bacteria, oxidizing it to NO 3 -. b. Consequently the predominant form of N available to roots is NO 3 -. C. Nitrification
A. NO 3 - must be reduced back to NH 4 + in order to be incorporated into organics. B. This process is energetically expensive but required. D. Nitrate Reduction
a. The actual incorporation of NH 4 + into organic molecules in the plant body. b. Process similar to that of an electron transport chain: c. Reduced N passes through a series of carriers that function repeatedly but in the long run are unchanged. d. Usually in roots E. Nitrogen Assimilation
2. Carnivorous plants A. Digest animals & insects – why? a. Grow in soils lacking an essential nutrient B. Motor cells! C. Trap insects & secrete digestive juices Ex. Venus flytrap, pitcher plant, Darlingtonia
3. Mycorrhizal relationships A. Fungus & plant roots B. Fungus gets carbos C. Plants get greater SA for water & phosphorus uptake D. Almost all plant species! E. 2 types: a. Ectomycorrhizae – hyphae form dense sheath over root; extend into cortex & out into soil. Thickened roots of woody plants b. Endomycorrhize – microscopic, more common.